Coccidiosis may be a major parasitic disease of poultry and causes a considerable economic loss in the poultry industry. The loss due to coccidiosis includes mortality, malabsorption, inefficient feed utilization, and impaired growth rate in broilers and a temporary reduction of egg production in layers. It was estimated that coccidiosis in the poultry industry in Great Britain caused a yearly loss of 61 million USD. By extrapolation, the global costs could be expected to be 2400 million USD per annum.
The genus Eimeria, a Coccidia subclass, belongs to spore-forming, unicellular, and obligate protozoa. That is to say, they must live and reproduce within animal cells. Eimeria is an intestinal parasite and can infect fishes, reptiles, birds, mammals. Of note, chickens are susceptible to at least 11 species of Eimeria. E. tenella, E. necatrix, E. brunetti and E. maxima are the more virulent species and E. acervulina, E. praecox and E. mitis are less virulent species in chickens. Eimeria infection is usually asymptomatic and however, shows severe clinical symptoms such as diarrhea, bloody droppings, dehydration, droopiness, listlessness, loss of appetite, paleness, ruffled feathers and huddling in young and immune-compromised animals.
The life cycle of Eimeria comprises intracellular, extracellular, asexual, and sexual stages. Once the chickens are infected with Eimeria, the parasites develop in the chicken and give rise to a microscopic egg (called an oocyst) which is passed out in the droppings. Under proper conditions of temperature and moisture the oocyst develops within one to two days to form a sporulated oocyst which is capable of infecting other chickens. At this stage the oocyst contains eight bodies (called sporozoites), each of which is capable of entering a cell in the chicken's intestine after the oocyst is eaten. When sporozoites enter the cells, they divide many times producing either a few or many offspring (merozoites). The numbers produced depend on the species of coccidia involved. Each merozoite in turn may enter another intestinal cell. This cycle may be repeated several times. Because of this cyclic multiplication, large numbers of intestinal cells are destroyed. Eventually, the cycle stops and sex cells (microgametocyte and macrogametocyte) are produced. Microgametocyte fertilizes macrogametocyte to produce and oocyst which ruptures from the intestinal cell and passes in the droppings. Thousands of oocysts may be passed in the droppings of an infected chicken. Therefore, poultry raised in crowded or unsanitary conditions are at great risk of becoming infected.
Vaccination and chemotherapeutic approach are currently used to prevent and treat coccidiosis. Live attenuated vaccines are used to prevent coccidial infection. Its advantage is lack of residual antibiotics in the chicken meat. However, the cross-species protection in coccidian vaccines is unsatisfactory. On the contrary, the most widely used compounds are the ionophore antibiotics, monensin, narasin, salinomycin, maduramicin, semduramicin and lasalocid, which prevent the development of first generation schizonts of the Eimeria genus. However, antibiotic-resistant Eimeria strains have recently been isolated. Moreover, the residual antibiotics in chicken meat have been a public health concern. Therefore, research and development of novel and safe anti-coccidial agent is practically significant. Plants are recognized as a wonderful source for human as well as animal medicines. Bidens pilosa, an Asteraceae family, is claimed as folk medicines for a variety of diseases.